There exist a number of wind turbine types or designs. A common type of wind turbine is the three-bladed upwind horizontal-axis wind turbine (HAWT), in which the turbine rotor is at the front of the nacelle and facing the wind upstream of its supporting turbine tower. Another type is the multi-rotor array type wind turbine, where a plurality of wind turbine modules are mounted to a common support structure.
EP1483501 discloses a multi-rotor array-type wind turbine in which a plurality of co-planar rotors are mounted to a common support structure. In general, a multi-rotor wind turbine may achieve the economy of scale that can be obtained with a very large single rotor turbine, but has the potential to avoid the associated drawbacks such as high blade mass, scaled up power electronic components and so on. Nevertheless, although such a co-planar multi-rotor wind turbine has its advantages, it presents challenges to implement the concept in practice, particularly in how to control the multiple rotors to achieve optimum power production. EP1483501 approaches the control strategy by treating each wind turbine of the system as a separate item that is controlled individually.
It is against this background that the invention has been devised.